1. Field of the Invention
This invention relates to a process of deasphalting an asphalt-containing mineral oil. More particularly, it relates to a process for obtaining a hydrocarbon oil with a low asphalt content. This invention especially relates to solvent deasphalting an asphalt-containing hydrocarbon feedstock with a liquid solvent.
2. Description of the Prior Art
Many petroleum crude oils contain significant quantities of asphalt. Asphalts have a boiling range which coincides with that of many of the higher boiling constituents of petroleum. Since asphalts readily oxidize to form carbon and sludge, their presence is undesirable in lubricating oils. Further, due to their high coking propensity asphalts must be excluded from fluid catalytic cracking units where high coke levels are detrimental to catalyst performance.
Solvent deasphalting has proven effective in providing low asphalt-content petroleum fractions and has been practiced commercially for many years. In these deasphalting processes, the oil dissolves in the selected solvent while the asphalt, which is present in a dispersed state in the mineral oil, precipitates during the solvent treatment. Propane deasphalting has proven to be one of the most commercially successful of these processes, especially in the preparation of high quality lubricating oils.
The prior art is replete with solvent deasphalting processes employing a variety of solvents and solvent mixtures. Typical of this prior art in U.S. Pat. No. 2,337,448 of Carr which discloses a process for deasphalting a heavy residuum by contacting it at elevated temperatures with a deasphalting solvent such as ethane, ethylene, propane, propylene, butane, butylene, isobutane or mixtures thereof. A number of other solvents and solvent combinations are disclosed in the patent art as being useful in solvent deasphalting, including a two or three component solvent selected from hydrogen sulfide, carbon dioxide and C.sub.3 -C.sub.5 hydrocarbons (U.S. Pat. No. 4,191,639 of Audeh et al.), propylene-acetone (U.S. Pat. No. 3,975,396 of Bushnell et al.) and naphtha or C.sub.3 -C.sub.5 hydrocarbons together with small amounts of ethane, ethylene, alcohols, esters or ketones (U.S. Pat. No. 2,045,742 of Winning et al.). U.S. Pat. Nos. 3,206,388 and 3,228,870 of Pitchford disclose the effectiveness of n-propyl alcohol or isopropyl alcohol containing a small quantity of water or a larger quantity of C.sub.5 -C.sub.15 n-paraffin as a deasphalting solvent for either a crude oil or a fraction thereof.
Bray et al. (U.S. Pat. Nos. 2,081,473 and 2,101,308) and Bray (U.S. Pat. No. 1,949,989) teach a wide range of solvents that will dissolve the oil and any wax in the oil but will not dissolve the asphalt. This extensive list includes liquified normally gaseous C.sub.2 -C.sub.4 hydrocarbons, naphtha, and casinghead gasoline, as well as alcohol, ether, mixtures of alcohol and ether, acetone and the like. Only the preferred liquified C.sub.2 -C.sub.4 hydrocarbons are exemplified, however.
C.sub.1 -C.sub.4 alcohols were employed in U.S. Pat. No. 3,364,138 of Van Lookeren Campagne to remove the resins from an oil-solvent solution after the asphalt had been precipitated from a residual petroleum stock by propane. Solvent extraction of the resins from asphalt by the use of alcohols was also the subject of U.S. Pat. No. 3,003,946 of Garwin (C.sub.3 -C.sub.4 aliphatic alcohols) and U.S. Pat. No. 2,726,192 of Kieras (n-butanol).
Solvent refining of coal tars often has involved the use of alcohols. In U.S. Pat. No. 3,079,326 of Neuworth, a double solvent extraction is employed. Aqueous methanol dissovles the acidic portion of the coal tar and then naphtha removes the neutral oils leaving a solid pitch phase. A solvent mixture of an aliphatic ketone and a lower alcohol, both having no more than six carbon atoms, (U.S. Pat. No. 1,905,423 of Rhodes et al.) as well as ethanol alone (U.S. Pat. No. 1,674,710 of Wittek) have also been employed to solvent extract coal tars. Methanol, alone, (U.S. Pat. No. 1,327,271 of Comber et al.) or as an aqueous solution (U.S. Pat. No. 3,153,626 of Kulik) has also found utility in coal tar extraction.
Although alcohols are disclosed broadly in the prior art as deasphalting solvents, only the propanols are specifically exemplified as having the ability to precipitate asphalt from the mineral oil while concomitantly dissolving the mineral oil. On the other hand, C.sub.1 -C.sub.4 alcohols and mixtures thereof when added to a deasphalted oil-solvent solution act as an anti-solvent precipating the resins. The only use of methanol (alone or with water) for the direct treatment of heavy carbonaceous materials in the prior art is to solvent extract coal tar. No specific use of methanol as a deasphalting solvent is disclosed.
The use of methanol as a deasphalting solvent for mineral oils may provide processing advantages not realized heretofore and this is the object of this invention.